The present invention relates generally to exposure, and more particularly, to an exposure apparatus and a manufacturing method of manufacturing various devices including semiconductor chips, such as ICs and LSIs, display devices, such as liquid crystal panels, sensing devices, such as magnetic heads, and image pickup devices, such as CCDs, as well as a fine pattern used for micromechanics. Here, the term micromechanics refers to technology for applying the semiconductor IC fabricating technique for fine structure manufactures, thereby, creating an enhanced mechanism system that operates at a level of a micron.
A conventional projection exposure apparatus uses a projection optical system to expose a circuit pattern of a mask (reticle) onto a wafer, etc., and a high-resolution exposure apparatus is increasingly demanded.
Since a minimum size (resolution) to be transferred by a projection exposure apparatus is in inverse proportion to the numerical aperture (“NA”) of a projection optical system, an improvement of the NA of the projection optical system is accelerated, and a development of a projection optical system having an NA of 0.9 is being promoted. However, a method that simply increases the NA of the projection optical system and improves the resolution has limits of a high NA scheme, because the depth of the focus (“DOF”) narrows in inverse proportion to the square of the NA, and the DOF necessary to manufacture devices is hard to assure in a higher NA scheme. Accordingly, the recent technological development attempts to obtain both a high resolution and a long DOF.
For example, one proposed exposure apparatus places a partially phase inverting pupil filter on a pupil plane or a Fourier transformation plane in the projection optical system for improved imaging performance. See, for example, Japanese Patent Application, Publication No. 07-037781. This exposure apparatus can thereby improve both the imaging performance and the DOF.
However, as a mask pattern increases an interval and becomes sparse (i.e., non-dense), not only does a 1st order diffracted light of the object spectrum, but also, a higher order diffracted light that has an antiphase to the first order diffracted light, enters the pupil, decreasing the DOF. When a pattern has an interval narrow enough for a dense pattern, a two-beam interference between the 1st order diffracted lights provides a desired DOF. However, as the pattern interval increases, a higher order diffracted light, which has an antiphase to the 1st order diffracted light, is incident, in addition to the ±1st order diffracted lights, and interferes with the ±1st order diffracted lights, disturbing imaging in defocus. The pupil filter of Japanese Patent Application, Publication No. 07-037781, normalizes a pupil radius to one, and inverts a phase in a range between r1<r<r2, where r is a radial position on the pupil plane, r1 being set to nearly 0.25, and r2 being set to nearly 0.92. This method has an increased DOF effect to a contact hole pattern, but decreases the DOF to a line pattern, to the contrary.
On the other hand, an alternating phase shift mask (“PSM”), which is often used to improve the resolution partially inverts a phase of the transmission light. However, even the alternating PSM poses the same problem as the mask pattern interval increases. There is no known method that can assure a similar DOF to both a dense pattern having a small pattern interval and a sparse pattern having a large pattern interval.